Success on the quiet

Rose Byrne says she likes to stay under the radar, meaning the kind of radar that zaps big stars on a minute-by-minute basis: she just wants to go to work on the train, muddle through market stalls, eat in cafes without being bothered.

So far, so good. As the ingenue end of television legal drama Damages, she entered the world's more discerning lounge rooms for 59 coruscating episodes alongside a devilish Glenn Close; as haughty Helen in Bridesmaids she was part of a comic phenomenon. Despite this - and thus quite surprisingly - the real Rose Byrne lives largely unscathed.

Byrne, 33, grew up in Balmain and got into acting via the very Australian route of kids' acting classes and TV soaps. She has lived in New York since 2007, after some itinerant years on the sets of some strikingly big films. Before Bridesmaids, she said 95 per cent of her fan mail came from Star Wars fans whose obsession with detail extended to her luminous bit part as Dorme, Natalie Portman's handmaiden in Attack of the Clones. ''I was kind of an extra in it,'' she said later, ''but I understand it's a big cult thing.''

One can only guess whether her new film, a romantic comedy written and directed by Sacha Baron Cohen's co-writer Dan Mazer, will get her more bother on the subway. I Give It a Year is about a marriage that is clearly disintegrating from the get-go, a phenomenon Byrne says she was surprised to discover was common. ''I had heard, prior to this, just from friends, that it was the hardest year,'' she says. ''You'd think it would be the honeymoon period but, in fact, it's not. So that really interested me, along with doing the lead in a romantic comedy - which I haven't done before.''

But there is nothing very comic about her character, Nat, a prim career girl who remains resolutely unsmiling while more-or-less funny things happen around her. ''She's kind of humourless, weirdly,'' Byrne says. ''She's not that good an audience, rather self-absorbed and not very observant, which is really the opposite of me - I'm from a family that laughs a lot.''

Nat's husband, Josh, played by Rafe Spall, is a potty-mouthed prankster. ''He would make me laugh constantly in the middle of a scene,'' she says. ''Dan was always saying 'You're getting on too well! You've got to chill out!'''

Byrne and the English Spall both play Americans in this film, as does Josh's competing love interest Simon Baker, another Australian actor who has become big on American television, in his case via The Mentalist. Was it odd to pretend to be American with another Australian? ''Yes and no,'' Byrne says. ''By the time Simon came in, I'd been there for three weeks doing my vocal coaching and I was already in the zone of the character. But yes, in that it's as surreal as anything else, walking round saying, 'Why are we doing anything?', you know.''

She still sounds entirely, if gently, Australian; recently she was in Perth to make one of a series of stories adapted from Tim Winton's book The Turning. Byrne was also asked to use her own accent in the forthcoming film The Internship, in which she plays an executive at Google. ''It was actually a bit strange. Something about doing an accent has become so much a part of my experience of acting that letting it go was unnerving. I had this whole thing in my head of how [the character] talked and I had to throw it away.''

Small wonder, maybe, that punters find it difficult to place her. For her part, she sees herself as a character actor, even if she does have - to quote Wolfgang Petersen, her director in Troy - ''the face of a Madonna''. One moment she's a no-nonsense pilot (Danny Boyle's Sunshine); the next, a flamboyantly sexed-up pop star (Get Him to the Greek, with Russell Brand).

''To be able to do a diversity of genres is great,'' she says. The point about acting as a child, she says, was that it was all about pretending, imagination and fun. And is it all that now? ''Hopefully I do still feel like that,'' she says. ''When I'm having a good day.''

I GIVE IT A YEAR

GENRE Romantic comedy.

CRITICAL BUZZ With only a smattering of trade reviews in, they range from the delighted - ''smart, witty and sometimes plain hilarious'', according to Screen Daily - to the mildly pleased. ''The irreverent IGIAY wants to mess with the genre … In a film with obvious ambition, it's a shame that it resorts to formula so quickly,'' remarked Total Film.

DIRECTOR Dan Mazer.

STARS Rose Byrne, Rafe Spall, Simon Baker, Anna Faris.

OPENS February 28.

RATED M.

Six Rose Byrne moments

Two Hands (1999) Byrne was 19 when she played opposite Heath Ledger in Gregor Jordan's story of young, averagely stupid criminals; the film launched all three of them into American careers.

The Goddess of 1967 (2000) Melbourne filmmaker Clara Law's movie won Byrne the Volpi Cup as best actress at the Venice Film Festival. ''It's a bit surreal," she said at the time. "They must have had slim pickings.''

Rage in Placid Lake (2003) Another best-actress award, this time from the Australian Film Institute, rewarded Byrne's turn as the smart girlfriend to Ben Lee's aspiring young capitalist.

Marie Antoinette (2006) Byrne moved temporarily to France to play the elaborately decorative Duchesse de Polignac in Sofia Coppola's distinctly Californian take on the Ancien Regime.

Get Him to the Greek (2010) An uncharacteristically brassy role as Jackie Q, a sex-on-legs pop star in the Aguilera mould opposite self-styled sex addict Russell Brand. "I had a blast with Russell," she said at the end of the shoot. "He's been a perfect gentleman."

Bridesmaids (2011) Byrne pitched for the role of shrill, controlling Helen, the matron of honour. "[My agent] said, 'You want to have a crack at the bitch?' I did," she told Marie Claire. "It was a project I would've killed to be part of." Stephanie Bunbury